The new app, which comes in iPhone and iPad flavors, are iOS-native, meaning that they can tap the hardware, adding features like gesture support and voice control. The native app approach also means it can be used when offline.

However, the iOS is available to Office 365 subscribers. Only customers with active Office 365 accounts can use OWA on the iPhone or iPad, even though the app itself is free to download from Apple's App Store.

In addition, Exchange Online is a requirement. Businesses that still run their own on-premise Exchange servers are out of luck for now.